All they've announced officially is that they'll announce it this financial year.
I wouldn't be surprised to see a similar pattern play out to that of the Switch, or even more compressed in terms of timeline.
They didn't officially confirm the release date of March 2017 until January 2017 (something like 6 or 7 weeks ahead of release), I would expect a similar 'late' announcement of release date, even if we see the console itself announced a bit sooner.
Given the Switch is still performing pretty well though and has a healthy batch of new software for the end of 2024, it wouldn't surprise me if they keep news of the successor quieter until 2025 anyway - it's a bit different to the situation with the WiiU which was dead on it's backside by 2016.